Electrolytic humidostat



y 1950 s. w. GILLINGHAM 2,510,018

ELECTROLYTIC HUMIDOSTAT Filed June 1a, 1947 MXW,

Patented May 30, 1950 ELECTROLYTIC HUMIDOSTAT Samuel w. Gillingham, Chicago, 111., asslgnor to Sears, Roebuck and 00., Chicago, 111., a corporation of New York Application June 13, 1947, Serial No. 754,452

8 Claims.

My invention relates to electrolytic humidostats of the general character described in Research Paper R. P. 1265, published as a part of Journal of Research of the National Bureau of Standards, vol. 23 page 701, December, 1939, entitled An improved electrical hygrometer, by Francis W. Dunmore.

Such devices were known before the Dunmore paper and are disclosed in several United States patents. In their common characteristics they comprise a base member which is usually of cylindrical shape and formed of or coated with an electrically non-conducting material which is non-adsorptive to water, on which support is wound bifllar electrical conductors, the latter being connected to a suitable electrical circuit for amplifying and registering variations in resistance. The element is coated with a thin film of an electrolyte which will absorb water from the atmosphere and thus form an electrolytic conductor between the wires.

The Dunmore paper, cited above, describes certain disadvantages of the previously known hygrometers as (1) long period aging, (2) hysteresis effect or short period aging, and (3) polarization, and then describes as Dr. Dunmores contribution to the art the discovery that "platinum and palladium wires were the only kinds that would eliminate this aging effect, and also the use of polystyrene coating to prevent hysteresis.

A particular object of my invention is to provide a hygrometer or humidostat which is specially adapted for controlling the ventilation in a dairy sbarn. Hence, while the work of Dr. Dunmore, as outlined above, is of interest in connection with my problem, it does not furnish a solution thereof for the reason that certain especially diilicult atmospheric conditions are encountered in a stock barn which were never considered by Dr. Dunmore, who was interested primarily in weather determination. In contradistinction to weather tests, where free and uncontaminated air is encountered, a stock barn encounters an atmosphere polluted with corrosive gases, such as ammonia, which seriously affect the operation of an instrument such as an electrolytic humidostat.

A particular object of my invention, therefore, is the provision of an electrolytic humidostat which will operate accurately for a relatively long period of time under the severe atmospheric conditions of a stock barn and under such conditions will avoid the aging effects mentioned in the Dunmore paper. More particularly, an object of my invention is to provide a combination as of electrolyte and wire which, when cooperating electrolytically, will not form a gas in an irreversible reaction.

After extensive research I have discovered an arrangement which completely solves this problem, and tests with a large number of humidostats embodying my invention under most severe conditions and variations of temperature and humidity, show operating characteristics which vary no more than one per cent.

One feature of my invention is that I employ a combination of wire which is either pure nickel or a nickel-chromium alloy, together with an electrolyte of nickel nitrate. I find also that, to avoid polarization, the size of the wire is important and should be of a gauge of #30 or larger.

As another feature of my invention, I have found that the best results are obtained when the coating of electrolyte is applied in aspecial way so that it is thicker on each pair of wires wound on the support than in the spaces between the pairs of wires; in other words, there is a wide thin film of electrolyte between the pairs and a narrow thick film on the pairs of wires. In this way the sensitive coating is so arranged that the resistance between the widely spaced elements of the coils is always much higher than the resistance between the closely spaced ones, due to the fact that the thin film does not hold as much moisture as that held by the thicker coating. As a result, the bifilar coil behaves substantially like two long, closely spaced, straight parallel wires with a finite number of parallel resistances between them. The resistance range of the spirally wound coil can be materially changed by changing the length of the wires used to wind it.

Referring more particularly to the drawing forming part of this specification and illustrating certain embodiments of my invention:

Fig. 1 is an elevational view of a humidostat embodying my invention,

Fig. 2 is a fragmentary sectional view taken substantially along the line 2-2 of Fig. 1, and

Fig. 3 is a plan view of a modified form of humidostat embodying my invention.

The numeral it indicates a cylindrical support which may be formed of a wide variety of materials, the desired characteristics being that it is electrically non-conducting and non-adsorptive to water. The preferred material is polystyrene but, if desired, I may use a cylinder formed of other material coated with polystyrene. The latter is an ideal material to serve as a base, but doubtless various other plastic or other materials having substantially equivalent physical 3 characteristics may be used. as indicated in the prior art. Wound onto the base In is a bifilar conductor l2 which is preferably arranged so that the spaces l5 between the pairs of wires are greater than the spaces l'l between the respective wires of each pair.

My preferred material for the conductors I2 is an alloy of nickel and chromium comprising 80 per cent nickel and 20 per cent chromium, such as is known in the trade as Nichrome. However, I am not restricted to this specific alloy and may use an alloy of nickel and chromium in various other ratios, or pure nickel. The preferred gage of wire is #30 or larger, inasmuch as I find that a smaller wire is likely to produce excessive polarization. Although I do not restrict myself to specific dimensions or proportions, I prefer to use It] bifilar turns in one inch on three-fourths inch diameter polystyrene tube of 1%; inches in length, the spacing between the bifilar turns being 0.02 inch. All leads inside the tube are coated with liquid polystyrene. The wires are connected to suitable terminals 20, 20 adapted to engage a socket member, as described below.

The wired form is dipped in a hygroscopically sensitized plastic comprising 15 grams of polyvinyl acetate dissolved in 175 grams of water and 1'75 grams of ethyl alcohol (denatured with 5 per cent methanol) with 3 percent by weight of nickel nitrate added as the sensitizing material. The form is plunged quickly into the liquid and withdrawn slowly so as to allow as much as possible of the material to cling to it.

The sensitive element thus formed is placed in the grid lead of a vacuum tube relay circuit with a slight electrical current passing through it, say about 5 micro-amps. The major change produced by this current is the decomposition of the nickel nitrate whereby nickel is deposited on the negative wire while the nitrate radical unites with hydrogen from the water vapor present to form nitric acid. This nitric acid slowly attacks the wires to form more nickel nitrate. Although in periods of relatively high current flow the element polarizes to a certain extent, upon a subsequent drop in current flow the element loses this polarization and regains its original operating point.

An element as described above'with 3 per cent nickel nitrate has an electrical resistance of 10,000 megohms at 37 per cent relative humidity. This resistance drops uniformly to 0.05 megohm at 77 per cent relative humidity. By changing the percentage of nickel nitrate, the same resistance range can be obtained at any desired relative humidity from 10 to 100 per cent. Thus a l per cent element shows 10,000 megohms at 17 per cent R. H. and 0.05 megohm at 55 per cent R. H., while a 6 per cent element gives 10,000 megohms at 10 per cent R. H. and 0.05 megohrn at 51 per cent R. H.

Fig. 3 illustrates an alternative form of hu-- midostat where, instead of employing a cylinder as a base, I use a disk of polystyrene or equivalent and wind the bifilar element 26 in a flat spiral instead of in a helix, as in the other embodiment. Otherwise, the conditions are as described with reference to Figs. 1 and 2, it being noted that the space between the pairs of conductors is greater than between the respective wires of each pair.

Various other changes coming within the spirit of my invention may suggest themselves to those skilled in the art, and hence I do not wish to be limited to the specific forms shown or uses mentioned, except to the extent indicated in the appended claims.

I claim:

1. An electric humidostat comprising a nonconductive and non-adsorptive support, bifilar conductors spirally wound thereon, the space between each pair of conductors being greater than the space between the units of each pair, and a film of hygroscopic electrolyte on said support and conductors, said film being of reduced thickness in the areas between the conductor pairs.

2. An electric humidostat comprising a nonconducting and non-absorptive support, bifilar conductors spirally wound thereon, and a film of hygroscopic electrolyte on said support and conductors, said electrolyte comprising a nickel compound and said conductors being formed of a metal of the class consisting of nickel and nickelchromium alloy.

3. A humidostat as defined in claim 2 wherein the electrolyte is nickel nitrate and the conductors are formed of nickel-chromium alloy.

4. A humidostat as defined in claim 1 wherein the electrolyte comprises a nickel compound and said conductors are formed of a metal of the class consisting of nickel and nickel-chromium alloy.

5. A humidostat as defined in claim 1 wherein the electrolyte is nickel nitrate and the conductors are formed of nickel-chromium alloy.

6. A humidostat as defined in claim 3 wherein the wire is a least as large as #30 gauge.

7. A humidostat as defined in claim 4 wherein the wire is at least as large as #30 gauge.

8. A device as defined in claim 1 wherein said coating material is relatively dry between the convolutions of said pair of conductors and is relatively moist between the members of said pair.

SAMUEL W. GILLINGHAM.

REFERENCES CCITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,295,570 Dunmore Sept. 15, 1942 2,398,333 Shoemaker Apr. 9, 1946 OTHER REFERENCES Mellors Chemistry, vol. 15, 1936, pages 48'7- 493. (Copy in Division 59.) 

